Crawling The Deep Web
A vast amount of Web pages lie in the deep or invisible Web. These pages are typically only accessible by submitting queries to a database, and regular crawlers are unable to find these pages if there are no links that point to them. Google's Sitemaps protocol and mod oai are intended to allow discovery of these deep-Web resources.
Deep Web crawling also multiplies the number of Web links to be crawled. Some crawlers only take some of the -shaped URLs. In some cases, such as the Googlebot, Web crawling is done on all text contained inside the hypertext content, tags, or text.
Strategic approaches may be taken to target deep-Web content. With a technique called screen scraping, specialized software may be customized to automatically and repeatedly query a given Web form with the intention of aggregating the resulting data. Such software can be used to span multiple Web forms across multiple Websites. Data extracted from the results of one Web form submission can be taken and applied as input to another Web form thus establishing continuity across the Deep Web in a way not possible with traditional web crawlers.
Read more about this topic: Web Crawler
Famous quotes containing the words crawling, deep and/or web:
“You know, Frank, Im beginning to get a new perspective on this crawling little animal known as man. Why a dog or a cat or a bird is cleverer than any human. They sense me immediately. But these shrewd detectives of yours. Take away one of mans senses and you render him helpless.”
—Lester Cole (19041985)
“Roll on, thou deep and dark blue Ocean,roll!
Ten thousand fleets sweep over thee in vain;
Man marks the earth with ruin,his control
Stops with the shore;”
—George Gordon Noel Byron (17881824)
“Thou blind mans mark, thou fools self-chosen snare,
Fond Fancys scum and dregs of scattered thought,
Band of all evils, cradle of causeless care,
Thou web of will whose end is never wrought;
Desire! desire, I have too dearly bought
With price of mangled mind thy worthless ware;”
—Sir Philip Sidney (15541586)